People search systems are known that search for a predetermined person based on a similarity calculated between a face image contained in a surveillance image captured by an image-capturing unit provided so as to be capable of capturing people passing through a certain location and a face image of the predetermined person.
In the conventional people search systems, however, when the face image in the surveillance image contains some factors, such as a mask or sunglasses, that inhibit the search for the predetermined person based on the face image, such factors lower the similarity between the face image in the surveillance image and the face image of the predetermined person, which results in lower search accuracy of the predetermined person. To prevent the lower search accuracy of the predetermined person, when the similarity threshold for determining the predetermined person is reduced, search errors of the predetermined person increase, which decrease efficient search for the predetermined person.